3.3 Redundancy analysis
The RDA plot showed that the first two axes jointly accounted for 93.9 % of the variance (Fig.4). The results showed that CAT activity of submerged plants in each group was negatively correlated with other physiological indexes. Root vitality was positively correlated with biomass, plant height, and root length. SOD activity was positively correlated with Chl-a, Chl-b, Chl-a+Chl-b, and MDA contents. The great distance among the substrate groups indicated that different substrates had different effects on the plants.